1. Field of the Invention
Embodiments of the present invention relate to a frame structure of a vehicle, such as a motorcycle.
2. Description of the Related Art
Conventionally, a body frame of a motorcycle including a head pipe supporting a steering shaft, and right and left main frames arranged extending rearward from the head pipe is available. A head pipe disclosed in Japanese Patent No. 4132431 includes a wall portion formed to extend rearward between right and left main frames. The wall portion has flange portions formed thereon, the flange portions projecting in a right-to-left direction to support the main frames from below. The wall portion also has flange portions formed thereon, the flange portions projecting in the right-to-left direction to define an interval between the right and left main frames. With this structure, frame strength is improved.
The head pipe disclosed in Japanese Patent No. 4132431 is formed integrally by forging, a process in which pressure is applied to a material from right and left sides of the material. Specifically, the pressure is first applied to the material from the right and left sides thereof to form a forged member having a columnar portion. After that, a hole for inserting the steering shaft is formed in the columnar portion by cutting work. By handling the forged member in this way, strength of the body frame is improved.